1. Field of the Invention
The present invention generally relates to devices used to repair and replace electronic components, and more particularly to a device used to replace surface mounted components.
2. Description of the Prior Art
During the past forty years, society has been experiencing an explosion in electronics technology. As electronic circuits became more complicated, engineers had a harder time trying to fit all of the components into a relatively small package. This problem was greatly mitigated by the introduction of transistors, which replaced the obsolete vacuum tube. Later, when integrated circuits were invented, computers and other electronic devices became even smaller. Now we are on the verge of the next evolutionary step in electronics packaging that will reduce standard electrical circuits by an order of magnitude or more, that of surface mount technology.
The foundation of modern electronics lies in the integrated circuit (IC) known as the dual in-line package (DIP). A DIP typically has metal leads that protrude from two sides of the chip, extending through a printed circuit board (PCB), with solder welds on the opposite side of the board. This combination appears in virtually all types of electronic systems ranging from supercomputers to television sets. A close examination of a PCB reveals that today's space problem does not lie in the size of the chip, but rather in it connections to the supporting circuitry. Surface mount technology may well force the celebrated DIP to join the vacuum tube in the annals of history.
Surface mount technology (SMT) simply refers to components that are mounted directly onto the surface of the board, without leads penetrating to the opposite side. The advantages of SMT are obvious. Higher component density may be achieved, and components may even be mounted on both sides of the PCB. SMT is not really new, as it has been used for years in digital wristwatches and slim pocket calculators. However, it has been projected that by the year 1990, 75% of all electronic equipment in the world will be manufactured by surface mounting.
SMT devices are typically installed using reflow soldering. In that technique, flux containing granulated solder is placed between the PCB and the SMT component. The flux (as well as the PCB and components) is then heated by convection, infra-red radiation, or vapor-phase penetration. The solder melts, fixing the component to the board. Excess resin is then removed with a suitable solvent.
At the present time there are three different kinds of surface mounted IC's. Those are the small outline integrated circuit (SOIC), the plastic leaded chip carrier (PLCC), and the leadless ceramic chip carrier (LCCC). With regard to the present invention, these three chips basically differ only in their lead structure. The leads of the SOIC extend outwardly to lie flat on the PCB. This structure has been termed "gull-wing." The PLCC, by contrast, has inwardly extending J-shaped leads. The LCCC has no leads at all, but rather has metallic contacts molded in its ceramic body.
The present invention is directed to the replacement and repair of SMT components. Since these components are mounted flush with no structural support, unique tools will have to be devised to allow removal of the component. As far as IC's go, the SOIC is the only surface mounted chip that may be removed using conventional soldering methods. Even this would be extremely difficult, however, as great care must be taken to avoid reflow of adjacent components. Moreover, the industry appears to be endorsing PLCC devices over the SOIC, as the PLCC has a smaller "footprint."
One tool recently developed for SMT repair is the heated collet. The heated collet is a tweezer-type iron, similar to existing DIP desolderers in that it completely clamps around the component and heats the entire unit, melting the solder in the process. This has the obvious disadvantage of destroying heat sensitive elements surrounding the defective component. The exposed heating elements can also cause damage to the human operator. Furthermore, a separate collet is required for each package size.
The present invention deals with a hot gas system for reworking surface mounted components. Hot gas systems are known for desoldering conventional (non-surface mounted) components. Some of these are shown in the following patents:
______________________________________ U.S. Pat. No. Inventor(s) ______________________________________ 4,295,596 Doten et al. 4,426,571 R. Beck 4,552,300 Zovko et al. 4,605,152 R. Fridman 4,610,388 Koltuniak et al. 4,620,659 J. Holdway 4,626,205 Barkley et al. ______________________________________
Each of the devices shown in these patents, however, suffers from the same critical drawbacks as the heated collet-the hot gas conduit presents a safety hazard to technicians, and the gas has a tendency to melt or otherwise damage surrounding components. It would, therefore, be desirable and advantageous to devise a hot gas system capable of removing any type of surface-mounted components which would not injure either adjacent IC's or the user of the system. The device should also economically accommodate a wide variety of SMT component sizes.